Arc-interrupting materials and apparatus

ABSTRACT

An arc-interrupting composition for the walls of electrical circuit interrupting devices to improve the characteristics of such device for interrupting high power circuits. The composition comprises melamine, and a thermoplastic organic binder which is more reactive to arcing than the melamine and under arcing conditions vaporizes or decomposes violently to drive the more stable melamine into the arc and thereby render the melamine effective. Improved effectiveness of the composition over a range or for particular applications may be obtained by adding other components, including melamine-formaldehyde resin, hydrated alumina, and fillers such as silica or aluminum fluoride.

United States Patent [72] inventor PaulW.Jones Lafayette, Ind. [21] Appl.No. 536,119 [22] Filed Mar.2l,l966 [45] Patented June1,1971 [73] Assignee RostoneCorporation Lafayette, Ind.

[54] ARC-INTERRUPTING MATERIALS AND APPARATUS 1 Claim, 3 Drawing Figs.

[52] U.S.Cl 200/144, 200/149, 174/137 [51] lnt.Cl H0lh 33/70, 1101b 9130 [50] FieIdofSearch ZOO/144.3, 149, 149.1; 174/137 [56] References Cited UNITED STATES PATENTS 2,526,448 10/1950 Amundson etal 200/l49(.1) 2,645,693 7/1953 Cole etal ZOO/144(3) 2,768,264 10/1956 JonesetaL. ZOO/144(3) 2,917,607 12/1959 Sterling 200/144(.3) 2,988,622 6/196] Petermichlet al 200/149(.l)

3,002,072 9/1961 Nava et al ZOO/144(3) 3,242,257 3/1966 Jones et al. 174/137 FOREIGN PATENTS 609,575 9/1960 ltaly ZOO/144.3

737,461 7/1943 Germany... 907,074 3/1954 Germany... 933,818 [0/1955 Germany OTHER REFERENCES German Printed Application No. E7152 V1llb/21c, published July 5, 1956 (Inventor: Groth) Primary Examiner-Robert S. Macon Att0rneyTrask, Jenkins & Hanley ABSTRACT: An arc-interrupting composition for the walls of electrical circuit interrupting devices to improve the characteristics of such device for interrupting high power circuits. The composition comprises melamine, and a thermoplastic organic binder which is more reactive to arcing than the melamine and under arcing conditions vaporizes or decomposes violently to drive the more stable melamine into the arc and thereby render the melamine effective. Improved effectiveness of the composition over a range or for particular applications may be obtained by adding other components, including melamine-formaldehyde resin, hydrated alumina, and fillers such as silica or aluminum fluoride.

PATENTEDJUN' 1 I911 IIOV 60 CyC I0.000 V E 1 7 Jo 1o{ INVENTOR PAUL W. JONES /ATTORNEYIS ARC-INTERRUPTING MATERIALS AND APPARATUS This invention relates to electrical circuit interrupting apparatus, and especially to arc-interrupting materials and apparatus embodying such materials.

It is a principal object of the invention to provide arc-interrupting materials and apparatus, which will have improved overall performance to quickly and positively interrupt power circuits and extinguish the arcs which occur upon separation of the conductors, over a wide range of voltages and amperages, and especially at high voltages and amperages, and which will give improved arc-interrupting performance while also meeting other necessary requirements, such as physical characteristics, nontracking properties, insulating characteristics, etc.

The invention is especially adapted for use in electrical devices in which interruption of the conductor path produces an are which tends to persist and to maintain current flow. These include, in particular, expulsion-type fuses and bayonet-type circuit interrupters, but the invention may also be used to advantage in many other interrupting devices in which a power are is generated and must be quickly interrupted or extinguished to effectively break the circuit.

When interrupting 60-cycle current, especially at high voltages, it is desirable and usually essential to interrupt the are within one-half cycle or less, that is, within one one hundredtwentieth second, for unless the arc is interrupted as the instantaneous current reaches zero value, the arc will tend to persist. For this purpose, for example, in expulsion-type fuses the conductor separation is made to occur in an arc zone which is closely surrounded by a confining tube or other housing, open at at least one end, composed ofa particular material which in the presence of the arc generates large quantities of gages quickly. Such gas generation aids in expelling the fuse-link parts, thus lengthening the arc, and the gas also desirably has arc-interrupting or extinguishing effects.

Various distinct materials or compounds have been used or proposed for such confining walls or tube. Horne fiber has been so long and widely used as to be a standard against which other materials are compared. Other materials which have been used include boric acid and various resins such as acrylic, acetal, nylon, polytetrafluoroethylene, etc.

In low and intermediate ranges of operation, the compositions of U.S. Pat. No. 2,768,264, especially compositions of hydrated alumina and a binder, are useful, and have found wide use in motor controls, circuit breakers, etc. Improved compositions containing hydrated alumina and addition agents as disclosed'in the copending patent of myself and Robert E. Wilkinson U.S. Pat. No. 3,242,257 are likewise of special value at low and intermediate ranges of operation. The teachings of those patents may be utilized in combination with the present invention.

I have found that one single compound or material is not the most suitable over the entire range of power that a device may be called upon to interrupt. ln a single type of device, such as an expulsion fuse, voltages may range from 2% KV to kv., and the current may range from 50 amperes to 5,000 amperes, and the same device may be called upon to interrupt power currents at various combinations of these voltages and amperes. While one material or compound may interrupt the arc efficiently at a given voltage and current, this same material may not be efficient or even effective over the entire range of operation.

I have discovered that improved overall operation and effectiveness over a wide range of voltages and currents may be obtained by a combination of materials. In accordance with the invention, 1 form a molded arc-confining element from a basic composition consisting essentially of (l) a material, preferably melamine, which is effective as an arc-interrupting material for very high power arcs but which is not highly efficient over the entire range of operation and particularly not efficient at low currents, and (2) a binder which is substantially more volatile and more unstable than such arc-interrupting material and which, in the presence of the arc, will rapidly volatilize or decompose to form a large volume of gas and to propel the arc-interrupting material with great force into the core of the arc. The binder is preferably one which itself has arc extinguishing characteristics.

In such basic composition, the preferred arc-interrupting compound is melamine, which is a chemical compound having the empirical formula C N H and which is thus composed largely of nitrogen. It occurs as a white crystalline powder having a melting point of approximately 350 C. but which sublimes at melting temperatures and below. its molecule is large and stable and these properties are believed to contribute to its arc-interrupting characteristics. It is proposed as an arc-interrupting compound, along with several related compounds in Amundson et al. U.S. Pat. No. 2,526,448. Melamine itself, however, has a number of deficiencies, notably its lack of effect at low power conditions and its extreme structural weakness which prevents it from being molded or pressed into satisfactory structural shapes.

The binder used in the basic composition should be one which volatilizes or decomposes violently in the presence of an electric are over a wide range of arcing conditions, especially under low power conditions below those in which melamine itself is highly effective. The effect of the combination may be visualized as one in which the more responsive binder drives the melamine with explosive force into the very core of the are, where melamine itself becomes effective; and one in which the combination of components produces large volumes of gas both for its expulsion effects and for its arc extinguishing effect under all ofa wide range of conditions.

in addition, the binder may be selected for its molding properties, and to give a structure of adequate physical strength, physical and chemical stability, electrical insulating properties, etc., which will vary with the application for which the material is intended. Further, and preferably, the binder may be selected for its own arc-interrupting properties. However, in certain applications the binder need not necessarily have the best quenching or noncarbonizing characteristics, since the melamine will provide quenching and in one-use devices with are chambers of low air volume, a carbonizing tendency may be of no great significance.

Various thermoplastic resins have been found satisfactory as binders. Particular binders which have been found satisfac tory include polyethylene, polypropylene, polytetrafiuoroethylene, acrylic, and acetal.

Melamine-formaldahyde resins, which are thermosetting, may also be used as a binder. However, if used in high percentage the resulting composition carbonizes quite readily under the influence of the electric arc. Improved arc-interrupting characteristics are obtained, particularly at low currents when melamine-formaldehyde resin is added as particles or powder in the composition along with thermoplastic binders. Other small-percentage additions, for example, of gas-producing compounds, are also contemplated.

The amount of binder used should be sufficient to provide the desired physical properties, and especially to provide the explosive propulsion of the melamine into the arc zone. The preferred proportion in the basic composition is 1 part binder to 2 parts melamine. On the basis of present information, I consider it desirable to have at least 10 percent and preferably 20 percent of binder, based on total composition.

The amount of melamine may also vary. On the basis of present information, I prefer to use melamine in the amount of not more than 90 percent, and desirably not more than about percent of the combined total of melamine and binder; and preferably at least about 50 percent of the total melamine and binder and at least about 30 percent of the total composition.

The composition must be chosen for the application; and the basic composition may be modified by the addition of other components to meet special conditions or to obtain an effectiveness pattern better suited to particular applications.

' As noted above, the addition of melamine-formaldahyde resin particles improves performance at low amperage circuit interruptions. While this produces a tendency to carbonize,

this may be of no importance where the arc chamber has small air space so that insufficient oxygen is present to react with the carbon.

If noncarbonizing is desired, the composition may contain hydrated alumina, which prevents carbonization if present in suitable proportions. The compositions may also include addition agents in accordance with the teachings of U.S. Pat. No. 3,242,257.

To improve operation at extremely high voltages and amperages, the composition desirably contains a proportion of finely divided inorganic filler, such as silica, SiO or aluminum fluoride, Al,F These have been found effective, and it is thought they act to physically absorb heat when projected into the arc, and also, by their vaporization, to remove considerable energy from the arc. Underrepeated operation, however, these tend to build up fused or sintered residues, and hence should be avoided in devices where the parts of arc-interrupting composition are required to slide on one another or on other parts, such as in the circuit interrupter of FIG. 2.

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a longitudinal sectional view of an expulsion-type fuse embodying my invention;

FIG. 2 is an isometric view of a bayonet-type circuit interrupter embodying the invention; and

FIG. 3 is a diagram of a laboratory testing device for evaluating arc-interrupting compositions in accordance with the invention.

The expulsion-type fuse shown in FIG. 1 is adapted for use in a conventional manner in a conventional fuse carrier. It comprises an outer rigid tube which may be of conventional vulcanized horne fiber, or a glass-reinforced molded tube, or other known type of expulsion-type fuse tube. At its upper end it carries a terminal collar 12 secured to the tube 10 by a pair of pins 14 and having an externally threaded upper end 16 for the reception ofa cap 18. Adjacent its lower end it carries a terminal clamp 20. The fuse comprises an upper headed fuse terminal 22 adapted to be removably clamped between the collar terminal 14 and the cap 18, and connected to the upper end of a strain wire 24 and a fuse wire 26. The lower ends of the strain wire and fuse wire are connected to a lower terminal 28 which is connected by a flexible conductor 30 to the clamp terminal at the lower end of the tube. The fuse is surrounded by a liner 32 which at its upper end is secured and sealed to the body of the upper fuse terminal 22 and which extends as a liner inside the fuse tube 10 for the entire length of the fuse wire 26 and for a distance beyond the lower fuse terminal 28. The liner is composed of an arc-interrupting composition in accordance with the present invention.

In operation, when the fuse blows, an arc is formed between the upper fuse terminal 22 and the lower fuse terminal 28, and such arc is closely confined and surrounded by the walls ofthe arc extinguishing liner 32. The are vaporizes the metal of the fuse wire 26 and strain wire 24 and causes the surface of the liner 32 to vaporize or break down with a rapid evolution of gases which expel the terminal 28 and the now free end of the flexible conductor 30 out of the fuse tube. This lengthens the arc path, and the gases act to extinguish the lengthened are. To renew the fuse, the cap 18 is removed, the fuse terminal 22 and liner 28 are withdrawn from the supporting outer tube 10, and a new fuse assembly and liner 32 are inserted and locked in place by the cap. The conductor 30 of the spent fuse is discarded and that of the new fuse assembly is connected to the clamp 20.

The circuit interrupter illustrated in FIG. 2 is for interrupt ing heavy power circuits It comprises an outer cylindrical shell 40 of a molded composition selected for its physical strength, lined with a molded tubular liner 42 of a composition selected for its arc-interrupting characteristics. At spaced points along its length, the tubular assembly carries a pair of contact units each consisting ofa fixed hollow stud 44 in which a contact 46 is spring pressed inward. For closing a circuit between the contacts, the shell assembly 4042 contains a slidable rod 48 which has a relatively close fitting relation in the liner 42. The rod comprises a shorting spool 50 having lands 52 spaced to engage with the spring-pressed contacts 46 and having its center portion surrounded by an insulating sleeve 54 and its ends fixed in end pieces 56. The sleeve and end pieces, like the liner 42 are of a composition having arc-interrupting characteristics in accordance with the present invention.

When the rod assembly 48 is moved to bring the lands 52 into registry with the contact members 46, a large-capacity electrical circuit is closed between the two contacts 46. To open that circuit, the rod assembly is drawn axially to carry the lands 52 out of registry with the contacts 46. When this is done, the arcs which form between the separating lands and contacts are drawn between the close fitting surfaces of the liner 42 and the insulating parts 54 and 56 of the rod, so that the physical confinement of the arcs, and the arc-interrupting characteristics of the material in those surfaces cooperate to interrupt the arc.

In the laboratory test apparatus shown in FIG. 3, the test specimen is molded in the form ofa tube 60 which is mounted in a suitable fixture to enclose a fixed electrode 62 and a movable electrode 64 which is cyclically moved into arc-striking contact with the fixed electrode 62 and withdrawn from such fixed electrode to lengthen the arc existing between the electrodes. The movement of the movable electrode 64 is actuated by a motor driven eccentric 66 connected to the electrode 64 by a link 68. The arc producing circuit is supplied with power from a volt, 60 cycle AC circuit 70 and the voltage is raised in a transformer 72 to 10,000 volts which is impressed across the two electrodes 62-64. An oscillograph 74 is connected to a transformer 76 across the electrodes 62- 64. The oscillograph measures the voltage drop across the arc as it is struck and extinguished. The oscillograph will show essentially no voltage when the contacts are closed; then, as the contacts open, the voltage drop across the arc increases until the arc extinguishes, and then the full voltage of 10,000 volts is registered across the contacts. The time the arc continues constitutes a representation of the power expended by the are before it is extinguished, and this represents, inversely, the efficiency of the arc extinguishing material of the surrounding tube 60. The duration of the arc is measured by the number of cycles of the 60-cycle current, and these can be counted on the oscillograph. In normal test use, 10 operations are carried out for each sample, and the results averaged.

Both in the case of the fuse tube liner 32 of FIG. I and the test specimen tube 60 of FIG. 3, it is the inner surface which is exposed to the arc and constitutes what may be termed an arcexposure surface, and it is this surface which should be composed of the arc extinguishing material in accordance with the present invention. In each instance, however, it may be convenient to mold the entire tube of such composition, and it is an advantage of the compositions of the present invention that they provide abundant strength and other physical properties for such elements as the fuse tube liner 32 or even of the fuse tube 10 itself. In the case of the arc-interrupting device of FIG. 2, the liner 42 of the tube 40 and the insulating parts of the sliding rod 48 may be molded of the arc-interrupting composition in accordance with the present invention.

The following examples illustrate the invention:

EXAMPLE I Melamine-Polyethylene Commercial-type expulsion fuse devices adapted for experimental testing were prepared with replaceable fuses 22-28 and replaceable arc extinguishing liner tubes 32 as indicated in FIG, 1 and the liners were molded of an arc-extinguishing composition in accordance with the invention.

In this example the basic composition was used, consisting of the following components and proportions by weight:

Melamine 6 parts Polyethylene 3 parts The dry components were mixed in a mechanical mixer and weighed charges were placed in a heated molding die and molded into tubes. The tubes and fuses were inserted in the fuse assemblies. The fuses were then tested-blownat l5 kv.

and at different amperages under controlled conditions. The fuses were found to meet the practical requirement of extinguishing the arc within one-half cycle of 60-cycle current, and the power expended by the are before its extinguishment was measured in kw.-seconds. The amount of erosion in the tube by the arc and the hot gases was then measured.

Corresponding tests were made using horne fiber as the material for the arc extinguishing liner, to provide a standard for comparison. Comparative test results are shown below in Table I.

At 300 amps, the arc was extinguished at 4.7 kw.-seconds with the home liner, and at only 2.6 kw.-seconds with the basic-composition liner of this example 1 of the invention.

At 1,500 amps, the are 1 was extinguished at 48.5 kw.- seconds with the home liner and at only 41.0 kw.-seconds with the liner of this example 1. The home liner lost 36.4 units (1X10 cubic in.) by erosion, or 0.75 units per kw.-second whereas the example 1 liner lost only 20.2 units by erosion, or 0.49 units per kw.-seconds.

EXAMPLE 2 Melamine-Polyethylene-Melamine Resin Commercial-type expulsion fuse devices were prepared and weight:

Melamine 6 parts Polyethylene 1 part Melamine-formaldahyde resin 2 parts Comparative test results are shown in table I.

The use of the melamine-formaldahyde resin as part of the binder gave higher erosion rates but improved the arc extinguishing result at 1,500 amperes. It also gave some improvement over the basic composition in 150 amperes tests.

ln single-operation fuse devices, the higher erosion is a permissible price to pay for improved operation.

Melamine-formaldahyde resin tends to carbonize in air under arcing conditions. Accordingly, this composition should not be used where carbonizing would produce arc tracks on multiple-use devices; or the carbonizing should be controlled by the addition of aluminum hydrate to the composition.

EXAMPLE 3 Melamine-PolyethyleneSilica Commercial-type expulsion fuse devices were prepared and tested as in example 1, but using a modified arc-interrupting composition of the following components and proportions, by

weight:

Melamine 3 parts Polyethylene 3 parts Silica 3 parts Comparative test results are shown in table 1.

The addition of finely divided silica improved the arc-interrupting characteristics at both 300 amps and 1,500 amps, and greatly reduced the erosion, especially at high amperages.

TABLEI Comparative Results of 15 kv. Tests ofCommercial-Type Fuses 300 Amp. [500 Amp.

Power Liner Power Liner Expended Erosion Expended Erosion During Cubic In. During Cubic In. Liner Arcing (l X 10 Arcing (1 X 10*) Material- KW-Sec. Per KW-Sec. KW-Sec. Per KW-Sec.

Home 4.7 48.5 .75 Example 1 2.6 None 41.0 .49 Example 2 2.6 1.6 35.0 .74 Example 3 1.9 .95 32.5 .13

*Not available.

EXAMPLE 4 Melamine-Polyethylene Test compositions were prepared containing different proportions of melamine and binder. Arc-interrupting tubes for test in the apparatus diagrammed in FIG. 3 were molded from the compositions and a series of (10) test evaluations were made with each composition. Power expended by the lengthening test arcs was indicated by the time period, in cycles of 60-cycle current, before the arcs were extinguished.

The proportions, by weight, and comparative test results of three such compositions are as follows:

Melamine 6 9 5 Polyethylene"..- 3 1 5 Are duration"... 6.4 11.9 13.4

Such tests indicate the preferred proportion of 6 parts melamine to 3 parts binder, such as polyethylene, in the basic composition; and that the desirable proportion-of binder is at least about 10 percent and less than about 50 percent of the combined melamine and binder.

EXAMPLE 5 Arc-interrupting materials of the compositions:

Example 5, Example 2, parts parts Melamine 6 6 Polyethylene 2 1 Melamine resin. 1 2

were molded into test apparatus tubes for test in the apparatus of FIG. 3. The test results indicated that the lower proportion of melamine resin was as effective as, or better than the formulation of example 2 at lower current conditions.

EXAMPLE 6 Arc-interrupting materials of other compositions involving. variations of the above examples include the following:

Melamine 5 6 Polyethylene 3 2 Melamine resin 1 Silica 1 2 position may include hydrated alumina in accordance with the teachings of U.S. Pat. No. 2,768,264. The amount of hydrated alumina should be sufficient to prevent carbonization of the binder, and preferably is used in amounts, by weight of from 50 percent to 100 percent or 150 percent of the amount of carbonizing binder.

To improve arc-quenching and especially to prevent ionization build up in multiple-use switching apparatus where arcs occur repeatedly in a chamber containing a substantial volume of air, the compositions of the present invention desirably include addition agents in accordance with the teachings of the copending U.S. Pat No. 3,242,257. 

1. An arc-interrupting composition which consists essentially of melamine and a binder, the binder comprises polyethylene or polypropylene and the composition contains approximately two parts melamine to one part binder, said binder being a thermoplastic material which is more responsive to electrical arcing conditions than melamine itself and in the presence of an electric arc vaporizes or otherwise decomposes violently, whereby to drive the melamine with explosive force into the arc and thereby render the arc-quenching properties of the melamine effective in the arc. 